Thermostatic coil



2 Sheets-Sheet 1.

(Nb Model.)

D. W. THOMPSON. THERMOSTATIG 0011,.

Patented Apr. 8, 1890..

THE mama PE (No Model.) 2 Sheets-Sheet 2.

D. W. THOMPSON.

THERMOSTATIG GOIL. No. 425,114. Patented Apr. 8, 189-0;

UNITED STATES I ATENT OFFICE.

DAVID W. THOMPSON, OF CHICAGO, ILLINOIS.

THERMOSTATIC COIL.

SPECIFICATION forming part of Letters Patent No. 425,114, dated April 8, 1890.

Application filed July 25, 1889- Serial No. 318,653. (No model.)

To all whom it may concern.-

Be it known that 1, DAVID W. THOMPSON, of Chicago, in the county of Cook and State of Illinois, have invented certain new and useful Improvements in Composite Strips for Thermostats and Similar Instruments; and I do hereby declare that the following is a full, clear, and exact description thereof, reference being had to the accompanying drawings, and to the letters of reference marked thereon, which form a part of this specification.

This invention relates to improvements in composite strips or coils for thermostats or similar instruments of that class which embrace composite strips consisting of two connected layers composed of substances having different degrees of expansibility under an increase in temperature.

The invention consists in the matters here inafter described, and pointed out in the appended claims.

In the accompanying drawings, illustrating my invention, Figure l is a front elevation of a thermostat-coil embodying the invention. Fig. 2 is a side view of the same. Fig. 3 is a sectional view of the strip composed of the coil, taken upon line 3 3 of Fig. 1. Figs. 4 and 5 are side views of the two layers composing the strip when the same are separate and before being bent into spiral form. Fig. 6 shows, in side view, the layers composing the coil after the same are secured together and before they are bent into spiral form. Fig. 7 is a sectional view, similar to Fig. 3, showing a sheet-metal layer bent or indented into a hardrubber layer for holding the layers from relative movement.

As illustrated in the said drawings, A is a thermostat-coil consisting of two strips or layers a a, of materials having different degrees of expansion under the influence of heat-as, for example, the exterior strip a may be of steel and the inner strip or layer a of hard rubber. The strip a is shown as attached at its inner end to a post B, by means of which the coil is sustained, said post being attached to any suitable support.

The particular means'of attaching the coil to the post herein illustrated consists of a transverse slot in the post, into which slot the inner end of the coiled strip is inserted and secured by riveting. At its outer end the coil is provided with a radial arm A, which may be located between two opposite contactpoints in the case of an electric valve-controlling or similar apparatus, or which may be connect-ed with any piece or part which is to be actuated by the moy'ement of the coil.

In the construction herein shown the arm A is formed by a continuation of the outer layer a of the coil; but said arm may be otherwise made-as, for instance, it may consist of a separate piece attached to the end of the coil. Oneof the strips or layers composing the coilthe layer Ct in the instance illustrated-is provided at its side margins with a series of teeth or prongs a M, which are bent around or over the margins of the other strip or layer a in such manner as to hold said strips or layers closely together.

In the operation of making the coil thus constructed the strips to and a are first prepared of the proper length. Said strips are then placed together and the teeth of the strip a then bent over or against the strip a, thereby holding said strips in contact with each other. The strips are then coiled and their ends permanent-1y secured to each other, the connection between the strips formed by the prongs a a obviously allowing the strips to slip upon each other endwise in the opera- ,tion of coiling, it being of course obvious that the inner strip or layer of the coil is shorter than the outer one.

In Fig. 6 I have shown the strips as prepared and placed together before coiling and after the teeth or prongs a a of the strip a are bent over thestrip a. Figs. 1 and 2 clearly show the coil after the springs have been connected together and bent to form a coil. The use of rivets as a means of fastening together the layers is not, however, essential, inasmuch as this may be accomplished in many different ways-as, for instance, the-teeth or prongs may be clamped or pinched against the edges of the strip embraced by them after the strips are coiled, with the effect of holding the strips from relative endwise movement.

The layer a, having the prongs (0 may be composed of any substance capable of being bent Without breaking. I find that sheet-steel serves well the purpose, and I prefer to use the same in connection with a second layer of hard rubber, these subsiances having a wide difference in expansibility umler the action of heat.

In the manufacture of thermostat-coils of the kind herein shown as heretofore conducted the two layers of material composing the spiral coil have been secured together by rivets disposed at short distances apart throughout the entire length of the coil. In making a coil of this kind the rivets must necessarily be inserted after the strips have been coiled or bent in acurved form, and, this operation has been found very difficult and troublesome, the rivets usually being inserted one after another as the coil is made, and, in asmuch as the curvature of the different parts of the coil depends upon the relative position of the holes through which the rivets are illserted, a coil thus made is commonly very irregular in shape, and liable, therefore, to operate with less accuracy than one which is uniformly curved.-

In a coil made as proposed by me the two layers are held together by the prongs or teeth in the manner herein set forth and are obviously adapted to slide one upon the other, and thereby adjust themselves to the curvature of the coil as the stripsare bent, thereby enabling a perfectly smooth, uniform, and synnnetrical coil to be easily made.

\Vhen one of the layers of the thermostatcoil is of metal and the other is of some other materialas, for instance, hard rubberthe teeth or prongs a a must of course be formed upon the metal part. \V hen both strips are of metal, however, the prongs may be formed upon either strip, or a portion of them upon one strip and a portion on the other strip, the general result being obviously the same as in the construction illustrated. \Vhen the external layer is of sheet metal and the other of hard rubber or some similar substance, the layers after being bent or coiled into spiral form may be held from relative movement throughout their entire length by indenting or pressing the sheet metal into the hard rubber at a number of points by the use of a pointed punch or similar instrument, such as has heretofore been used for similar purposes. A construction of this kind is shown in Fig.

7, wherein the metal is indented through the points or prongs thereof and at points opposite said points or prongs, as clearly indicated at a a in said Fig. 7. Said indentation is made after the metal is bent into spiral form by asuitable implement having prongs or jaws adapted for insertion between the coils. It is not essential, however, that indentations of this kind should be formed in said prongs, and they may be made elsewhere in the metal strip with good effect.

It will commonlybe preferred to secure the extreme ends of the layers by rivets in the manner hereinbefore described, even when the said layers are held together by clamping or pinching the prongs of the outer layer against the inner layer or by indenting the sheet-metal outer layer against an inner layer of hard rubber or similar substance, as shown in Fig. 7; but in some cases the use of the rivets may not be found necessary.

I claim as my invention- 1. A composite strip for thermostats and similar instruments, comprising two layers, one of said layers having teeth or projections at its side edges which embrace theside margins of the other layer, substantially as described.

2. A coil for thermostats and similar instruments, consisting of a composite strip comprising two layers of di tferent substances, one of said layers having teeth or projections at its side edges, which are bent over the side margins of the other layer to hold the layers together, substantially as described.

33. A coil for thermostats or similar instruments, ()Ollllll'lSlllg two layers, one of said layers being of hard rubber or other similar substance, aud the other layer of sheet metal and having prongs or teeth at its side edges, which are bent over the edges of the layer first mentioned, said metal layer being indented or pressed into the said hard-rubber layer at a plurality of points, substantially as described.

In testimony that I claim the foregoing as my invention I affix my signature in presence of two witnesses.

DAVID W. THOMPSON.

Witnesses:

(l. CLARENCE POOLE, HARRY Conn KENNEDY. 

